بهسازي خاكهاي واگرا با آهك با نگرش ويژه به كاهش شدت قله هاي اصلي كاني هاي رسي در پراش پرتو ايكس

Dispersive soil improvement with lime, special attention to the

وجود خاكهاي واگرا در محل اجراي سازههاي مهندسي، از مشكلات اساسي در برخي از پروژههاي عمراني است. پژوهش حاضر به مطالعه بهبود خصوصيات مهندسي خاك واگراي طبيعي با نگرش ويژه به تغييرات ريز ساختاري و حل شدگي قله هاي اصلي كاني هاي رسي و تشكيل تركيبات جديد مي پردازد. خاك مورد مطالعه داراي 100 % پتانسيل واگرايي است. در اين پژوهش ابتدا پتانسيل واگرايي خاك تعيين شده، و سپس خصوصيات مهم ژيوتكنيكي خاك مطالعه شده آزمايشگاهي قرار گرفته- است. در ادامه، خاك مطالعه شده با آهك شكفته مخلوط شده و بعد از پايان دوره عمل آوري، نمونه ها تحت آزمايشهاي مختلف ژيوتكنيكي قرار گرفته و ميزان تغييرات پتانسيل واگرايي و بهبود ويژگي هاي مهندسي خاك ارزيابي شده قرار گرفته است. همچنين روند تغييرات ريزساختاري نمونه ها شامل حل شدگي كانيهاي رسي و تشكيل تركيبات جديد در اندركنش خاك واگرا و آهك تحليل شدهاست. نتايج نشان ميدهد كه پتانسيل واگرايي در نمونههاي تثبيت شده كاملاً حذف شدهاست. همچنين نتايج آزمايش مقاومت فشاري محدود نشده و تحكيم نشان دهنده افزايش مقاومت و كاهش ميزان ضريب فشردگي است . بر اساس نتايج ارزيابي پراش پرتو ايكس علت اصلي بهبود خواص مكانيكي حل شدگي كاني هاي رسي، واكنشهاي پوزولاني و تشكيل تركيبات سيليكاتي و آلوميناتي كلسيم است. مهمترين نتيجه پژوهش حاضر را ميتوان تعيين درصد بهينه آهك بر اساس ميزان افزايش تنش % پيش تحكيمي و آزمايشهاي ريز ساختاري بيان نمود، كه به ازاي افزودن 6 درصد آهك ميزان تنش پيش تحكيمي حدود 430 50 افزايش نشان دادهاست. (kN/m افزايش يافته و به ازاي هر درصد آهك تنش پيش تحكيمي حدود

Civil engineering projects usually require an improvement on soil properties. In this case, the improvement of soil strength, permeability, and erosion resistance, collapsible or dispersive behaviour might be important. Consequently, engineers are always willing to achieve an optimum way to stabilize/improve soil performance for practical applications. Generally, the presence of dispersive clays in engineering projects is one of the essential problems for civil engineers. Several failures in engineering projects due to the presence of dispersive soils are reported in different parts of the world. In spite of several researches on this subject, there has been little attention to the microstructure of stabilized dispersive soils. In this paper the improvement of properties of a natural dispersive soil is studied with special attention to the solubility of clay mineral peaks in XRD analysis and formation of aluminates and silicates minerals after lime application to dispersive soil. The soil sample of this area is silty clay which has 100% dispersivity potential. Several geotechnical erosions are reported in this area which is attributed to the presence of dispersive soils. Due to the low bearing capacity of soil, and to overcome to its dispersivity behaviour, the application of lime is chosen as soil stabilization means. In this paper, at the first step with application of double hydrometer and cation exchange capacity experiments, the dispersive potential of soil is determined. In addition, the major minerals of soil are addressed by the use of XRD analysis. For the dispersive soil sample, the major geotechnical properties of soil including unconfined compression test, settlement behaviour, and over consolidation stress are measured and reported. Then, the soil sample is mixed with lime and water. After equilibrium and after curing process, several geotechnical and geo-environmental experiments were performed on soil samples to investigate on the dispersivity potential variations of soil. Furthermore, the microstructure of lime treated dispersive soil was monitored by application of XRD analysis on lime treated soil. The results indicate that the dispersivity potential of soil disappears after application of 6% of lime. In this process the dispersive structure of soil changes to the more flocculated structure. Moreover, the results of XRD analysis indicate that following application of lime, parts of clay fraction solubilize, leading to the formation of pozzolanic components. The main conclusion of this paper is the determination of the required percentage of lime for soil stabilization with the application of micro-structural experiments and with the measurement of the quantity of increase in over-consolidation stress. With the performance of several consolidation tests on untreated and lime-treated dispersive soil, it is shown that with application of 6% lime, an increase of 430% in over-consolidation stress is observed. This means for each percent of lime a 50 kN/m2 increase in over-consolidation stress is achieved.